Assionob to gael f



W. E. LAIDLEY.

ELECTRICSIGNAL SYSTEM.

APPLlCATlON FILED JUNE 2.191s.

Patented Aug. 26, 1919.

Jzzzrezizaf.

. UNITED STATES PATENT OFFICE.

WILLIAM E. LAIDLEY, or CLEVELAND, oi'rro, ASSIGNOR TO (mm. 1'. MEAD, or CLEVE- LAND, OHIO.

' ELECTRIC SIGNAL SYSTEM.

Specification of Letters latent.

Patented Aug. 26, 1919.

Application filed June 2, 1916. Serial No. 101,821.

To all whom it may concern:

Cleveland, in the county of Cuyahoga and State of Ohio, have invented certain new and useful Improvements in ElectricSlgnal Systems, of which the following is. a specification.

This invention relates to electric alarm systems, and more particularly to signal call systems wherein a desired signal may be produced by the central station operator s1- mul-taneously at a plurality of surrounding stations. Such systems, as commonly installed, comprise acomplete outfit of central and subordinate station equipment with the necessary wires for connecting up the stations, together with a suitable power source.

The object of this invention is to reduce the cost of and simplify such systems by eliminating the installation of special wiring circuits, This is accomplished by taking advantage of ordinary power circuits already installed, not only for the purpose of con-- meeting the substations to the central station,

but also, when desirable, as a source of power for operating the system, thereby .decreasing the initial cost of installation and the charges for maintaining the system in.

operation.

In the drawings Fig. 1 illustrates diagrammatically one embodiment of the invention, including both the sending and receiving sets; and Fig. 2 is a similar view of a modified form of the receiving circuits.

The invention is particularly applicable for use in department stores, banks, manufacturing plants, and other large buildings where it is necessary to reach an officer or employee who moves about from place to place. For example, if such person is called upon the telephone it is usually necessary to send a messenger through the plant for him or call up in turn the various branch telephone stations until he is found. This obj ection has been overcome to some extent by call systems embodying a central operating station (usually manipulated by the branch telephone exchange operator) and a number of sub-stations distributed throughout the plant. Actuation of the central station mechanism operates the signals at all substations; and by providing a different indication for each oflicer or employee liable to be so called he can be immediately notified, if within sight or hearing of a substation, that he is wanted at the central station.

Instead of providing a separate extensive wiring system connecting all the substations to the central station the present invention preferably utilizes a wiring system or power .circuit already installed such, for example, as an electric lighting clrcuit operating on direct or alternating current, a telephone or telegraph circuit or the wires of a fire alarm system. Such circuits ordinarily extend throughout the entire plant or building so that substations may be connected thereto wherever desired. If such a circuit is not at hand it can of course be installed for the production of its customary functions and thehpresent alarm system combined therewi-t v The invention may also be used in connection with a. telephone exchange system, for example in a small town, for simultaneously calling all of the firemen from their homes to the engine house.

In the drawings PC represents such a power circuit, say an incandescent lamp circuit, connected to a suitable power source S and provided with the usual sockets for the lamps 1. A is any suitable semi-automatic sending device for producing the various signals to be transmitted over the line. Said device, as illustrated, is of well known form and does not require more than a brief description. It may be hand operated but is shown as driven by a motor connected to the line, said motor driving a shaft 2 on which are a number of con-tact devices 3, any one of which may be selectively coupled to the shaft to rotate therewith and, in a complete rotation, to close a circuit B one or more times in a definite order. The particular construction of this circuit breaker or ,sending device forms no part of the present invention and is not essential. It may, for example, be of the construction illustrated and described in a prior Patent No. 1,249,162, granted December 4, 1917, to Carl F. Mead, although any other suitable form may be used. Said circuit includes a resistance R, which may be a lamp, and the primary L of a transformer whose secondary Ls is in'circuit with a'capacity O capable of absorbing a charge of several thousand volts potential from the secondary Ls at each alternation. The source S may be any suitable producer of low frequency alternations and is shown as a direct current generator, .in which case the circuit B also includes a suitable constantly operating me chanical interrupter I of fifty, more or less, interruptions per second, each impulse thereby transmitted serving to charge the ca acity C as will be readily understood.

he capacity C when charged, discharges across a ga CT and through an inductance L Gap 1 is adjustable as to the spacing of its electrodes, and the capacity C and inductance L 'are so selected or adjusted as to produce high frequency alternations or oscillations in their circuit, preferably at a frequency of about one million, more or less, per second. Said oscillations are of course slightly damped and unaffected by other constants than the inductance and capacity. The oscillatory circuit G G L has its inductance inductively associated with an additional inductance L connected in series with a capacity C in a circuit suitably connected to the power circuit over which the various signals are to be transmitted. This power circuit may be a circuit separate from the one which furnishes the current for producing the oscillations described but is shown as the same circuit PG, and the oscillatory current produced by the sendlng apparatus is superimposed .in said power circuit upon the normal current flowing therein to produce its ordinary functions, but the two currents are so essentially distinct in character as not to interfere in any way with each other.

The two circuits G G L and C L PC, are preferably in resonance with each other. In other words the product of the inductance and capacity of the first circuit is equal to the product of the effective inductance and capacity of the second circuit and for this purpose, in a general sense, the capacity of the power circuit PC may be con sidered infinite and its inductance zero.

The sending apparatus so far described produces a series of groups of forced oscillations in the power circuit PC each time the circuit B is closed at the sending device A, the frequency of said oscillations depending upon the tuning factors of the oscillatory circuits. Said oscillations extend throughout the entire circuit PC and are capable of being intercepted 0r detected and utllized at one or any number of points thereon by merely plugging into the power circuit a proper receiving set now to be described.

Each receiving set comprises a primary circuit connected across the power circuit PC and including an inductance L and capacity C in series, said circuit being tuned to the frequency of the oscillation circuits of the sending apparatus. The inductance L is preferably of a small number of turns 'inductances are also so arranged that the induced and applied electromotive forces in L are cumulatlve and not opposing. Inductance L is in a secondary circuit shunted across the inductance L and capacity C and also includes a small tuning condenser C and a large capacity C with a value of about one or two microfarads. with capacity C" is a winding W, which may be utilized to actuate a relay or any suitable signal device, either audible or visible, but which winding is shown as a solenoid arranged to attract an armature X to operate the single stroke gong Y. In parallel with the tuning condenser C is a gap Gr of ex-- tremely small length and large area to cool its electrode surfaces. Condenser C may be adjustable for tuning purposes to secure as nearly as possible close resonance between the primary and secondary circuits.

Capacity C has three functions; first, it serves as a by-pass for the high frequency oscillating current whose flow is otherwise impeded or-retarded by the choking effect of the bell winding W; second, it causes sufficient current to flow in phase with the electromotive force of PC to keep the gap G ruptured and acts as a storage reservoir of energy; and third, with the winding W it produces a condition of unit power factor of energy drawn from the power circuit by the winding W and capacity C".

Experience has shown that the resistance of a circuit is not the same for alternating currents of very high frequency as it is for direct current or currents of low frequency, and moreover, that the effective resistance of a circuit is not a direct function of the frequency therein. In the present system, assuming the power circuit to operate on direct current, before rupturing the gap Gr none of the normal current in the ower circuit can flow to the bell winding but, at the proper point in the voltage wave the potential in the secondary circuit created by the proportions of the capacity, inductance and gap length therein is suflicient to rup ture said gap and allow the current from the power circuit to flow to the capacity C*. As soon as the delicate gap is ruptured the large quantity of energy flowing to the capacity C maintains the ruptured condition of said gap long enough to allow suflicient current to flow through said gap to the capacity C and bell winding W to actuate the signal, such as by attracting the armature X and ringing the gong.

If the current in the power circuit is alternating current at low frequency, say 60 cycles per second, the tuning condenser C is In parallel so small that infinitely small current flows from the power circuit to the secondary circuit prior to rupturing the gap G and said gap is ruptured only when the high frequency alternations emanating from the source are superimposed upon the low frequency current in the power circuit to produce the necessary potential at the proper point in the voltage wave to rupture the gap and allow a material flow of energy from the power circuit to the secondary circuit.

The high frequency oscillating current is of high potential across the gap G or in the secondary circuit, but is low in amperage, so that it does not have sufiicient power of itself to actuate the signal but is merely depended upon to serve in conjunction with the low frequency or direct current to break down the delicate gap blocking the power from the power circuit to the signal winding W so as to allow the normal direct or low frequency alternating current at high amperage to reach the winding'W for actuating the signal.

In the system so far described the power circuit PO serves as the source of energy for actuating the signal, it being assumed that said circuit is normally an active circuit, such as a lighting or telephone circuit connected throughout the day to its power source. Said power circuit ma however, be

a normally, inactive circuit with no power at times flowing therethrough, and the power for actuating thesignal may be derived from a separate and distinct source. Such an arrangement is shown in Fig. 2, in which the secondary circuit of the receiving set is inductively instead of conductively connected to the power circuit. As shown the coupling is effected by the associated inductancesL L as before, inductance L being in series with the capacity C in a circuit connected across the power circuit PC. The secondary circuit of the receiving set includes in series with inductance L a separate power source S* which may be a battery or any other suitable source of electrical energy. The gap, tuning condenser, large capacity and bell winding are of the same form and arranged in the same manner as inthe system before described.

In the system last described the current from the source S is blocked from the winding W by the gap and tuning condenser and also cannot flow to the line PC. However, when the high frequency oscillations are transmitted to the power circuit they flow through the inductance L and induce oscillations in the secondary circuit through the inductive couple L L Said induced oscillations in the secondary circuit serve to ruptween said and superimposing the same upon and causing it to flow in a circuit connected to a source ofpower and to a signaling device in such manner as to complete a path for the flow of said alternating current, and utilizing said alternating current to complete a path for the flow of power from said power circuit to actuate said signaling device.

2. A signaling method, consisting in producing high frequency alternating current at a sending station connected to a circuit in turn connected to a source of power, superimposing said alternating current upon the current in said power circuit, and causing said alternating current to rupture a gap bepower circuit and a signaling circuit, whereby power from said power circuit flows to the signal circuit for actuating a signal therein.

3. A signaling apparatus, comprising a power circuit, a source of electric power connected thereto, means at one station in said power circuit for producing high frequency alternating current and superimposing the same upon the current flowing therein, and a signaling device at another station of said power circuit operated bythe power'of said circuit and controlled by the flow of said high frequency alternating current therethrough. v

4. Signaling apparatus, comprising a power circuit, a source of current connected thereto, means at one station of said power circuit for producing high frequency alternating current therein, a signal device at another station of said power circuit connected thereto through a gap, and means whereby the high frequency alternating current breaks down said gap and completes its own metallic path to cause current from said source to flow to the signaling device for actuating the same In testimony whereof I affix my signature in presence of two witnesses.

WILLIAM E. LAIDLEY.

Witnesses;

G. O. FAR UHAIsON, ELBERT L. HYDE. 

